1. Field of the Invention
The present invention relates to a light-emitting module. More particularly, the present invention relates to a light-emitting module, an optical alignment method for the light-emitting module, and an assembly method for the light-emitting module, in which an automated process is used to simplify and enhance the precision of optical alignment and assembly of the light-emitting module.
2. Description of the Related Art
A conventional optical output device, such as a printer or a photocopier, uses a light-emitting module to emit a light image on a photosensitive drum, such that the photosensitive drum generates an electric potential to adsorb carbon powder. The adsorbed carbon powder is subsequently transferred to paper. Lasers and light-emitting diode (LED) arrays are examples of light sources used by the light-emitting module. Compared to the more traditional laser-type output device, the LED array-type output device is smaller, allows for faster printing and copying, and has a lower cost.
Referring to FIGS. 1 and 2, a conventional light-emitting module 1 utilizing an LED array as a light source includes a housing unit 11, a light-emitting unit 12, and a lens unit 13. The housing unit 11 includes an outer housing 111 and extends along a direction (X) and having an approximately U-shaped cross section, and an inner support 112 mounted within the outer housing 111 and also extending along the direction (X). The light-emitting unit 12 is mounted within the outer housing 111 and extends along the direction (X). The light-emitting unit 12 includes a substrate 122, and a plurality of light-emitting elements 121 disposed on the substrate 122 and arranged spacedly along the direction (X). The lens unit 13 is inserted into a groove 1121 formed along a top face of the inner support 112. The light generated by the light-emitting elements 121 passes through the lens unit 13 and is focused onto an imaging plane 2 (e.g., on a photosensitive drum).
Since the resolution of the optical output device to which the light-emitting module 1 is applied is determined primarily by the accuracy with which the imaging plane 2 is realized, it is extremely important that the light-emitting unit 12 and the lens unit 13 be aligned precisely. In the conventional light-emitting module 1, optical alignment adjustment is performed manually. Such manual adjustment is referred to as “active alignment.”
Inactive alignment, the outer housing 111, the inner support 112, and the light-emitting unit 12 are first combined into a single assembly. The light-emitting elements 121 are subsequently driven to produce light. Next, using a charge-coupled device (CCD) on the imaging plane 2, a spot size of the light passed through the lens unit 13 and focused and irradiated onto the CCD is observed. Finally, in a state where the light-emitting unit 12 and the CCD are fixed in position, the relative positioning between the light-emitting unit 12 and the lens unit 13 is manually adjusted along six degrees of freedom (along the X, Y, and Z axes and rotational) until the optimum optical quality is obtained. The lens unit 13 is subsequently adhered to the inner support 112 in this optimum position, thereby completing optical alignment and assembly. However, such a conventional optical alignment and assembly method has the following drawbacks:
1. Such manual active alignment in the six degrees of freedom is a slow process. For example, 20 to 25 minutes maybe required to assemble and align each light-emitting module 1. This increases the cost of producing the light-emitting module 1.
2. During optical alignment of the lens unit 13 along the six degrees of freedom, a complicated six-axis control mechanism is needed. Further, during testing, it is necessary to utilize an illumination control module for driving the light-emitting unit 12. Also, a highly precise and stable measurement platform is required. All this translates into higher production costs for the conventional light-emitting module 1.